BetterThe previous article was about outdoor air, traffic, industry, power stations, the things a city measures. It killed 4.2 million people in 2019.
There is a second half of the problem, and it happens indoors while someone makes dinner.
2.1 billion people, about a quarter of humanity, cook on open fires or inefficient stoves burning kerosene, wood, animal dung, crop waste or coal.
“In poorly ventilated dwellings, indoor smoke can have levels of fine particles 100 times higher than acceptable.”
It was responsible for 2.9 million deaths in 2021, including more than 309 000 children under five.
The exposureA hundred times, indoors
Outdoor air quality is discussed in fractions above a limit. Indoors, the multiplier is of a different order.
And it produces the same diseases as the outdoor kind. WHO lists them in the same order: “stroke, ischaemic heart disease, chronic obstructive pulmonary disease (COPD) and lung cancer”cardiovascular first again, lung cancer last again.
ProximityWho sits closest to the fire
Exposure to household air pollution is not distributed by geography alone. It is distributed by who does which task.
“Exposure is particularly high among women and children, who spend the most time near the domestic hearth.”
WHO ties this to household work, and notes that reliance on polluting fuels and technologies “also require significant time for cooking on an inefficient device, and gathering and preparing fuel”.
The cost is therefore counted twice: in health, and in hours.
And the gap is rural. In 2021, 14% of urban dwellers used polluting fuels and technologies, against 49% of the world's rural population. Thirty-five points between two addresses.
ArithmeticTwo numbers that must not be added
This section exists because we made the mistake ourselves, in the previous article, and fixed it after reading this fact sheet.
Outdoor air pollution: 4.2 million deaths (2019).
Household air pollution: 2.9 million deaths (2021).
Sum: 7.1 million.
WHO's published combined figure: 6.7 million.
The total is lower than the sum on purpose. The same people breathe both kinds of air, and counting them once in each column would count them twice.
It is the kind of error that reads as rigour: two official figures, one subtraction, a tidy result. Nothing about the arithmetic warns you that the two populations overlap, only the third figure does, by being smaller than it should be.
The trajectoryWhat the current pace delivers
The fact sheet ends on a projection, and it is the least ambiguous sentence in it.
“At current rates, only 78% of the global population is expected to have access to clean cooking by 2030. This shortfall would leave nearly 1.8 billion people still without clean cooking solutions.”
Universal access to clean cooking by 2030 is part of Sustainable Development Goal 7. The sentence above is WHO stating, in advance, by how much it will be missed.
Which is the honest shape of this half of the subject. The solutions are named and unglamorous, solar, electricity, biogas, liquefied petroleum gas, natural gas, alcohol fuels, and biomass stoves meeting WHO emission targets. There is no discovery pending. There is a distribution problem, counted at 1.8 billion people.
QuestionsFrequently asked questions
How many people cook with polluting fuels?
“Around 2.1 billion people worldwide (around a quarter of the global population) cook using open fires or inefficient stoves fuelled by kerosene, biomass (wood, animal dung and crop waste) and coal, which generates harmful household air pollution,” WHO writes.
How polluted is the air indoors?
WHO writes that “in poorly ventilated dwellings, indoor smoke can have levels of fine particles 100 times higher than acceptable”.
How many deaths does it cause?
“Household air pollution was responsible for an estimated 2.9 million deaths per year in 2021, including over 309 000 deaths of children under the age of 5.”
Can these deaths be added to the outdoor ones?
No. 4.2 million (outdoor, 2019) plus 2.9 million (household, 2021) is 7.1, but WHO's published combined figure is 6.7 million. The total is lower than the sum because the same people are exposed to both and would otherwise be counted twice.
Who is most exposed?
WHO is explicit: “exposure is particularly high among women and children, who spend the most time near the domestic hearth.” Its key facts add that women and children, “typically responsible for household chores such as cooking collecting firewood, bear the greatest health burden”.
Is this an urban or a rural problem?
Overwhelmingly rural. “In 2021, only 14% of people in urban areas relied on polluting fuels and technologies, compared with 49% of the global rural population.” A gap of 35 points.
Read nextRelated
Sources
- Household air pollution, World Health Organization, updated 16 December 2025
- Ambient (outdoor) air pollution, World Health Organization, updated 24 October 2024
About this article. General and educational information, not medical advice. The figures come from the World Health Organization fact sheet on household air pollution, updated 16 December 2025; the data are for 2021. The outdoor figure (4.2 million) is for 2019 and comes from a different fact sheet. These two figures do not add up: the article explains why.
Spotted an error or an out-of-date figure? Write to us: we will correct it and re-date the article. Our texts are written with the help of artificial intelligence and checked against official sources before publication, but a figure or a definition can change without us catching it. If anything here does not match what an official body tells you, they are right.